Water heating and water cooling devices are well known and are widely used for providing water for use at a desired temperature.
Such devices generally include a water system having water inlet and outlet ports. Water at one temperature is passed into the system through the inlet port; is subjected to cooling or heating by way of apparatus installed within the system, depending on whether the system is a water cooler or a water heater; and is passed out of the system through the outlet port at approximately the temperature at which it is sought to be used.
In one type of device such as described above, the water system is a water tank containing water cooling or heating apparatus.
A disadvantage of a device that includes a water tank is that water that is sought to be heated, for example, enters the tank at a relatively low temperature and mixes with water that has already been heated to a relatively high temperature. It will be appreciated that this constitutes an inefficient way of heating water as the relatively warm water inside the tank is cooled by the relatively cool water entering the tank.
Similarly, in the case of a water cooling system, water that is sought to be cooled enters the tank at a relatively high temperature and mixes with water that has already been cooled to a relatively low temperature. It will be appreciated that this constitutes an inefficient way of cooling water as the relatively cool water inside the tank is heated by the relatively warm water entering the tank.